U.S. patent application number 10/582164 was filed with the patent office on 2007-06-28 for av system, av unit and image signal output method.
Invention is credited to Yoshiya Fujishiro.
Application Number | 20070150925 10/582164 |
Document ID | / |
Family ID | 34703273 |
Filed Date | 2007-06-28 |
United States Patent
Application |
20070150925 |
Kind Code |
A1 |
Fujishiro; Yoshiya |
June 28, 2007 |
Av system, av unit and image signal output method
Abstract
During receipt of an analog broadcast, when an instruction to
switch broadcast channels is received, an MPEG encoder (31)
subjects a broadcast signal for the switched channel to MPEG
encoding, and initially immediately sends MPEG data having one GOP
made up of only one I picture to an MPEG decoder (32). The MPEG
decoder (32) decodes this MPEG data (32), and a decoded video
signal is output to a video signal output section. After that, the
video signal output section (34) displays a still picture image
signal on a display etc. until a moving image corresponding to a
signal normally encoded/decoded is received.
Inventors: |
Fujishiro; Yoshiya;
(Kawasaki-shi, JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO LLP
1825 EYE STREET NW
Washington
DC
20006-5403
US
|
Family ID: |
34703273 |
Appl. No.: |
10/582164 |
Filed: |
September 30, 2004 |
PCT Filed: |
September 30, 2004 |
PCT NO: |
PCT/JP04/14807 |
371 Date: |
June 8, 2006 |
Current U.S.
Class: |
725/93 ;
348/E5.097; 348/E5.108; 386/E5.001; 725/115; 725/145 |
Current CPC
Class: |
H04N 21/431 20130101;
H04N 21/658 20130101; H04N 21/4325 20130101; H04N 9/8042 20130101;
H04N 5/50 20130101; H04N 21/426 20130101; H04N 21/4383 20130101;
H04N 21/433 20130101; H04N 5/76 20130101; H04N 21/6377
20130101 |
Class at
Publication: |
725/093 ;
725/115; 725/145 |
International
Class: |
H04N 7/16 20060101
H04N007/16; H04N 7/173 20060101 H04N007/173 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 2003 |
JP |
3003-417138 |
Jul 16, 2004 |
JP |
2004-210022 |
Claims
1. An AV network system comprising: an AV server (1) provided with
a receive section (11) for receiving an analog broadcast signal, an
encoder (12) for encoding the analog broadcast signal received by
the receive section (11) in MPEG form, and a network interface
section (13) for transmitting data encoded by the encoder via a
network (3), and an AV client unit (2) provided with a network
interface section (21) for receiving data transmitted via the
network (3), a decoder (22) for decoding MPEG data received by the
network interface section (21), an output section (23) for
outputting an image signal decoded by the decoder (22), and a user
interface section (24) for receiving an instruction to switch a
channel of a broadcast signal received by the receive section (11)
of the AV server (1) from a user, wherein when the user interface
section (24) receives an instruction to switch the broadcast signal
channel from the user, the encoder (12) encodes a switched channel
analog broadcast signal received by the receive section, to
initially create MPEG data made up of one GOP consisting of one I
picture, the decoder (22) decodes data made up of the one GOP
consisting of one I picture received via the network (3) and
encoded by the encoder (12), and the output section (23) outputs an
image signal for a still picture decoded by the decoder (22).
2. An AV unit, comprising: a receive section (30) for receiving an
analog broadcast signal; a user interface section (35) for
receiving an instruction to switch a channel of a broadcast signal
received by the receive section (30) from a user; an encoder (31)
for encoding a switched channel analog broadcast signal received by
the receive section (30) in MPEG form, when the user interface
section (35) receives a channel switching instruction from the
user, to initially create MPEG data made up of one GOP consisting
of one I picture; a decoder (32) for decoding the data encoded by
the encoder (31); and an output section (34) for outputting an
image signal for a still picture decoded by the decoder (32).
3. The AV unit according to claim 2, wherein: the decoder (32) is
provided with a buffer memory (32a) for storing MPEG data sent from
the decoder (31); and the decoder (32) decodes MPEG data made up of
one GOP consisting of one I picture stored in the buffer memory
(32a), and sends the decoded image signal for a still picture
repeatedly to the output section (34).
4. The AV unit according to claim 3, wherein: the decoder (32) is
provided with a buffer memory (32a) for storing MPEG data sent from
the decoder (31); and the decoder (32) discards data stored in the
buffer memory (32a) when the user interface section (35) receives a
channel switching instruction.
5. The AV unit according to claim 4, wherein: the decoder (32)
discards data stored in the buffer memory (32a), and discards data
received before receipt of data made up of one GOP consisting of
one I picture from the encoder (31).
6. The AV unit according to claim 2, wherein: the decoder (32) is
provided with a buffer memory (32a) for storing MPEG data sent from
the decoder (31); and the decoder (32) stores data received
consecutively with the data made up of one GOP consisting of one I
picture in the buffer memory (32a), and decodes the data to output
the MPEG data made up of one GOP consisting of one I picture stored
in the buffer memory (32a) until a given amount of data has been
accumulated in the buffer memory (32a).
7. The AV unit according to claim 2, wherein: the decoder (32) is
provided with a buffer memory (32a) for storing MPEG data sent from
the decoder (31); and the decoder (32), after decoding data made up
of one GOP consisting of one I picture, stores data received
consecutively with the data in the buffer memory (32a), and
sequentially decodes the data to output the image signal so that a
frame of the decoded image signal is interpolated.
8. An AV unit, comprising: a receive section (30) for receiving an
analog broadcast signal; a user interface section (35) for
receiving an instruction to switch a channel of a broadcast signal
received by the receive section (30) from a user; and an encoder
(31) for encoding a switched channel analog broadcast signal
received by the receive section (30) in MPEG form, when the user
interface section (35) receives a channel switching instruction
from the user, to initially create MPEG data made up of one GOP
comprising of smaller numbers of pictures than that of before
receiving said switching instruction.
9. An image signal processing method, comprising: receiving an
analog broadcast signal; receiving an instruction to switch a
channel of a broadcast signal to be received from a user; encoding
a received switched channel analog broadcast signal in MPEG form,
when a channel switching instruction is received from the user, to
initially create MPEG data made up of one GOP with one I picture;
decoding the encoded data; and outputting an decoded image signal
for a still picture.
10. An image signal processing method, comprising: receiving an
analog broadcast signal; receiving an instruction to switch a
channel of a broadcast signal to be received; encoding a received
switched channel analog broadcast signal, when a channel switching
instruction is received from the user, to initially create MPEG
data made up of one GOP comprising of smaller numbers of pictures
than that of before receiving said switching instruction; decoding
the encoded data; and outputting an decoded image signal for a
still picture.
Description
TECHNICAL FIELD
[0001] The present invention relates to an AV (Audio Visual) system
an AV unit and an image signal output method for receiving an
analog broadcast signal and outputting an image signal.
BACKGROUND ART
[0002] Recently, AV systems having an AV server for receiving
analog broadcast signals for television (TV) broadcasts and an AV
client unit for outputting images and sounds of the broadcast
signals received by the AV server for viewing have become
widespread. With these AV systems, the AV server receives and
encodes analog content data. The AV client system decodes data
taken in via a network from the AV server and outputs decoded data
to a display and speakers.
[0003] In this type of AV system, the AV server is provided with a
TV tuner for selecting a TV broadcast channel and receiving an
analog broadcast signal, and receives an analog broadcast signal
that has been tuned to by the TV tuner under control of the AV
client unit. The AV server encodes the received broadcast signal
using MPEG (Moving Picture Experts Group) encoder, and the encoded
content data is transmitted via a network to the AV client
unit.
[0004] The AV client unit is provided with a user interface section
for receiving instruction input from a user. The AV client unit
controls the TV tuner of the AV server according to instruction
input from the user interface section, and can select a TV
broadcast channel to be viewed by the AV client unit etc. The AV
client unit also receives encoded content data from the AV server,
decodes the content data and outputs decoded signals (video
signals, audio signals) to the display and speakers. A user watches
and listens to the images and audio by means of the display and
speakers.
[0005] With this AV system, an MPEG encoder of the AV server and
the MPEG decoder of the AV client are respectively provided with
buffer memory. The buffer memory of the MPEG encoder stores video
data for at least the number of pictures contained in a GOP (Group
Of Pictures), in order to generate an I picture (Intra-coded
picture), P picture (Predictive-coded picture) and B picture
(Bidirectionally predictive-coded picture) of the GOP of the MPEG
data. The buffer memory of the MPEG decoder temporarily stores data
so that reproduction is not interrupted even if there is a
temporary interruption in the MPEG data stream when reproducing
each picture of the GOP.
[0006] In this way, therefore, since the MPEG encoder and MPEG
decoder respectively store data temporarily in each buffer memory,
there is a corresponding time lag from receipt of the broadcast
signal to output. This type of time lag may be particularly
prominent when switching channels.
[0007] For example, when the user switches channels, the AV server
switches channels based on a channel switch instruction from a user
received by the AV client unit. During the period from channel
switching to image signal output, encoding by the AV server and
decoding by the AV client unit are carried out. Since the MPEG
encoder and the MPEG decoder temporarily store respective data,
there may be cases where a few seconds time lag is generated from
when the user switches channels until the image output to the
display is switched.
[0008] In the event that the user inputs an instruction to switch
channels, the user would like to immediately view the desired
channel, but the above-described time lag due to switching of
images causes a sense of discomfort to the user, and there may also
be cases where the user feels unpleasant in operability.
[0009] As a method for reducing this type of unpleasant feeling
experienced by the user, there has been developed a television
receiver where, when switching channels, information based on an
electronic program guide (EPG) for the channel to be switched to is
temporarily displayed on the display, while audio is output to the
speakers by decoding audio signals for the channel after switching
in advance (for example, Unexamined Japanese Patent Application
Publication laid-open No. 2001-339663: hereafter referred to as
patent document 1).
[0010] There has also been developed a receiver and image
reproduction method for temporarily displaying an image previously
prepared in a storage region of storage means in the receiver when
switching channels (for example, Unexamined Japanese Patent
Application Publication laid-open No. 2002-176599: hereafter
referred to as patent document 2).
[0011] There has also been developed a decoding circuit for storing
an I picture, B picture and P picture for a selected program from
within multiplex digital image signals in a decode buffer, storing
an I picture for non-selected programs in an intra buffer, and,
during a period from the time point where a program is switched
until the I picture for the newly selected program is received,
outputting the I picture for the intra buffer (for example,
Unexamined Japanese Patent Application Publication laid-open No.
Hei 9-247686: hereafter referred to as patent document 3).
DISCLOSURE OF THE INVENTION
[0012] However, even with the techniques disclosed in patent
document 1 and patent document 2 described above, it is impossible
to display an image for a channel desired by a user in a short time
after switching channels. Also, because different information
(image) is displayed for each channel switch, an uncomfortable
feeling and an impression of bad usability is given to the
user.
[0013] In particular, when frequently switching channels with
confirming the channel image, unrelated images are displayed each
time when the channel is switched, which is troublesome. Also, it
takes time until a user locates a desired channel, and operability
is poor.
[0014] The disadvantages of this point can be resolved according to
the technique disclosed in patent document 3. However, this
technique is only effective when receiving multiplex digital
broadcast signals. In other words, since only data for one channel
is contained in one frequency, it is not possible to apply this
technique with an analog broadcast.
[0015] As described above, the problems based on the time lag from
receipt of an analog broadcast signal until output are not limited
to the above described AV system, and also exist in an AV unit
provided internally with an encoder and a decoder for carrying out
digital processing of an analog broadcast signal and outputting an
image signal.
[0016] In view of the above-described situation, the present
invention is useful in providing an AV system, AV unit and image
output method having good ease of use.
[0017] The present invention is also useful in providing an AV
system, AV unit and image output method capable of digitally
outputting a switched image in a short time, when switching analog
broadcast channels.
[0018] An AV system of a first aspect of the present invention is a
network system, including an AV server provided with a receive
section for receiving an analog broadcast signal, an encoder for
encoding the analog broadcast signal received by the receive
section in MPEG form, and a network interface section for
transmitting data encoded by the encoder via a network, and an AV
client unit provided with a network interface section for receiving
data transmitted via the network, a decoder for decoding MPEG data
received by the network interface section, an output section for
outputting an image signal decoded by the decoder, and a user
interface section for receiving an instruction to switch a channel
of a broadcast signal received by the receive section of the AV
server from a user, wherein, when the user interface section
receives an instruction to switch the broadcast signal channel from
the user, the encoder encodes a switched channel analog broadcast
signal received by the receive section, to initially create MPEG
data made up of one GOP consisting of one I picture, the decoder
decodes data made up of the one GOP consisting of one I picture
encoded by the encoder, and the output section outputs an image
signal for a still picture decoded by the decoder.
[0019] An AV unit of a second aspect of the present invention
includes a receive section for receiving an instruction to switch a
channel of a broadcast signal received by the receive section from
a user, an encoder for encoding a switched channel analog broadcast
signal received by the receive section, when the user interface
section receives a channel switching instruction from the user, to
initially create MPEG data made up of one GOP consisting of one I
picture, a decoder for decoding the data encoded by the encoder,
and an output section for outputting an image signal for a still
picture decoded by the decoder.
[0020] With the above described AV unit, the decoder may also be
provided with buffer memory for storing MPEG data sent from the
decoder, and the decoder may decode MPEG data made up of one GOP
consisting of one I picture stored in the buffer memory, and send
the decoded image signal for a still picture repeatedly to the
output section.
[0021] With the above described AV unit, the decoder may also be
provided with buffer memory for storing MPEG data sent from the
decoder, and the decoder may discard data stored in the buffer
memory when the user interface receives a channel switching
instruction.
[0022] With the above described AV unit, it is possible for the
decoder to discard data stored in the buffer memory, and to discard
data received before receipt of data made up of one GOP consisting
of one I picture from the AV server.
[0023] With the above described AV unit, the decoder may store data
received consecutively with the data made up of one GOP consisting
of one I picture in the buffer memory, and decode the data to
output the MPEG data made up of one GOP consisting of one I picture
stored in the buffer memory until a given amount of data has been
accumulated in the buffer memory.
[0024] With the above described AV unit, the decoder, after
decoding data made up of one GOP consisting of one I picture, may
store data received consecutively with the data in the buffer
memory, and sequentially decode the data to output the image signal
so that a frame of the decoded image signal is interpolated.
[0025] An image signal output method of a third aspect of the
present invention includes receiving an analog broadcast signal,
receiving an instruction to switch a channel of a broadcast signal
to be received, encoding a received switched channel analog
broadcast signal, when a channel switching instruction is received
from the user, to initially create MPEG data made up of one GOP
with one I picture, decoding the encoded data, and outputting an
decoded image signal for a still picture.
[0026] An AV unit of a fourth aspect of the present invention is
provided with a receive section (30) for receiving an analog
broadcast signal, user interface section (35) for receiving an
instruction to switch a channel of a broadcast signal received by
the receive section (30) from a user, and an encoder (31) for
encoding a switched channel analog broadcast signal received by the
receive section in MPEG form, when the user interface section (35)
receives a channel switching instruction from the user, to
initially create MPEG data made up of one GOP consisting of smaller
numbers of pictures than that of before receiving said switching
instruction.
[0027] An image signal processing method of a fifth aspect of the
present invention includes receiving an analog broadcast signal,
receiving an instruction to switch a channel of a broadcast signal
to be received from a user, encoding a received switched channel
analog broadcast signal, when a channel switching instruction is
received from the user, to initially create MPEG data made up of
one GOP comprising of smaller numbers of pictures than that of
before receiving said switching instruction, decoding the encoded
data, and outputting an decoded image signal for a still
picture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The invention will now be described by way of example with
reference to the accompanying drawings, throughout which like parts
are referred to by like references, and in which:
[0029] FIG. 1 is a diagram illustrating the structure of an AV
system according to the first embodiment of the present
invention;
[0030] FIG. 2 is a flowchart for explaining operation of the AV
system of the first embodiment of the present invention;
[0031] FIG. 3 is a graph showing a lapse of time from channel
switching to start of image display for the AV network system of
the first embodiment according to the present invention and an AV
system of the related art;
[0032] FIG. 4 is a diagram illustrating the structure an AV unit of
the second embodiment according to the present invention;
[0033] FIG. 5 is a diagram illustrating the structure an AV unit of
a modified example of the second embodiment according to the
present invention; and
[0034] FIG. 6 is a diagram illustrating the structure of an AV unit
of a modified example of the second embodiment according to the
present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment
[0035] A first embodiment of the present invention will be
described in detail below with reference to the drawings. The
embodiment shown below is only one example, and is not
limiting.
[0036] In the first embodiment shown below, description will be
given relating to processing of a video signal for operation after
channel switching of an analog TV broadcast. Also, in order to
facilitate understanding, description relating to audio signals is
omitted.
[0037] FIG. 1 is a diagram illustrating the structure an AV system
100 of a first embodiment according to the present invention. The
AV system 100 shown in FIG. 1 includes an AV server 1 and an AV
client unit 2. The AV server 1 and the AV client unit 2 are
connected via a network.
[0038] First of all the AV server 1 will be described. The AV
server 1 is provided with a TV tuner 11, an MPEG encoder 12, a
network interface section 13 and a control section 14.
[0039] The TV tuner 11 is connected to an antenna 11a, and receives
an analog TV broadcast signal of a given frequency via the antenna
11a. The TV tuner 11 outputs a received broadcast signal to the
MPEG encoder 12. Under control of the control section 14, the tuner
11 selects a broadcast station (frequency) to be received based on
a receive station selection instruction received from an AV client
unit, that will be described later.
[0040] The MPEG encoder 12 carries out encoding by subjecting an
analog broadcast signal output from the TV tuner to digital
compression processing using an MPEG method. Encoded MPEG data is
output to the network interface section 13. The MPEG encoder 12 is
provided internally with a buffer memory 12a.
[0041] As will be described in detail below, at the time of
encoding immediately after switching receive station, data of at
least frames (for example, 15 frames) of one GOP (Group Of
Pictures) of MPEG data is stored in the buffer memory 12a in order
to create an I picture (Intra-coded picture), P picture
(Predictive-coded picture) and B picture (Bidirectionally
predictive-coded picture).
[0042] The network interface section 13 is connected to the AV
client unit 2, that will be described later, via a network 3. Under
control of the control section 14, the network interface section 13
transmits and receives control data such as channel select
instruction information, and control data etc. for carrying out
data transmission via the network 3 between the AV client unit 2
that will be described later. The network interface section 13 also
transmits MPEG data that has been input from the MPEG encoder 12 to
the AV client unit 2, that will be described later.
[0043] The control section 14 comprehensively controls the AV
server 1. As will be described later, when control data including
channel select instruction information has been received from the
AV client unit 2, the control section 14 controls the TV tuner 11
so that a broadcast signal for an instructed broadcast station is
received based on the channel select instruction information. In
the event that channel select instruction information has been
received, the control section 14 controls the MPEG encoder 12 so as
to stop encoding processing in the MPEG encoder 12, and discard
data currently being encoded and data stored in the buffer memory
12a.
[0044] Next, a description is given of the AV client unit 2. The AV
client unit is provided with a network interface section 21, an
MPEG decoder 22, a video output section 23, a user interface
section 24 and a control section 25.
[0045] The network interface section 21 is connected to the AV
server 1, via a network 3. Under control of the control section 25,
the network interface 21 transmits and receives control data such
as channel select instruction information based on a channel switch
instruction input from the user interface section 24, which will be
described later, and control data for carrying out transmittal of
data via the network 3, to and from the AV server 1. The network
interface section 21 also receives MPEG data that has been received
from the AV server 1 and outputs to the MPEG decoder 22.
[0046] The MPEG decoder 22 carries out decoding by subjecting MPEG
data input from the network interface section 21 to expansion
processing. A decoded video signal is output to the video output
section 23. The MPEG decoder 22 is internally provided with a
buffer memory 22a, and the buffer memory 22a stores MPEG data
transmitted from the AV server 1. The MPEG decoder 22 decodes MPEG
data stored in the buffer memory 22a and outputs to the video
output section 23.
[0047] As will be described in detail later, when the user
interface section 24 receives instruction input for channel
switching, the control section 25 changes the operation mode of the
MPEG decoder 22 from normal mode carrying out normal decoding to
channel switching mode for carrying out decoding when switching
channels.
[0048] The video output section 23 encodes a video signal output
from the MPEG decoder 22 according to a display system for the
display 4, and outputs the encoded video signal to the display
section 4. The display 4 displays an image on a screen based on the
video signal output from the video output section 23.
[0049] The user interface section 24, for example, receives an
instruction signal corresponding to an instruction input as a
result of a user operating a remote control 24a, and outputs this
instruction signal to the control section 25. Using the remote
control 24a, etc., the user inputs an instruction to switch a
broadcast station of a TV broadcast being watched, or an
instruction to change the volume, etc., to the user interface
section 24.
[0050] The control section 25 comprehensively controls the AV
client unit 2. As will be described in detail later, when the user
interface section 24 receives an instruction signal for channel
switching, the control section 25 transmits channel select
information via the network interface section 21 to the AV server
1, and changes the operation mode of the MPEG decoder 22 from
normal mode to channel switching mode.
[0051] Operation of an AV system of a first embodiment will be
described below with reference to the drawings. The embodiment
shown below is only one example, and is not limiting as long as the
same effects can be obtained.
[0052] A flowchart for explaining operation of the AV system
according to the first embodiment is shown in FIG. 2. With the
example shown in FIG. 2, description will be given for operation in
the case where, when the AV server 1 receives an analog TV
broadcast signal and MPEG encoded data is transmitted to the AV
client unit 2, the AV client unit 2 receives a channel switching
instruction from the user.
[0053] When the user is using the AV system 100, the AV server 1
receives an analog broadcast signal for a specified channel and
creates MPEG data by carrying out encoding. The AV client unit 2
receives MPEG data via the network 3 and outputs a decoded image
signal to a display 4.
[0054] In this state, the user operates the remote control 24a to
input a channel select command, to switch from a channel currently
being received to another channel, to the AV network unit 2. The
user interface section 24 receives this channel select command and
transmits an instruction signal to the control section 25 (step
S1).
[0055] If an instruction signal for a channel select command is
received from the user interface section 24, the control section 25
changes the processing mode of the MPEG decoder 22 from normal mode
to channel switching mode (step S2). The MPEG decoder 22 transmits
control data for the channel select instruction information from
the network interface section 21 through the network 3 to the AV
server 1 (step S3).
[0056] Here, the normal mode refers to a mode for sequentially
decoding a received MPEG stream. Also, the channel switching mode
refers to a mode for signal processing, described in the following,
from switching of a channel until outputting a broadcast signal for
the switched channel.
[0057] After switching, the MPEG decoder 22 stops decode processing
when completing decode processing of MPEG data for one GOP
currently being decoded and then discards data stored in the buffer
memory 22a (step S4). The MPEG decoder 22 waits until an MPEG
stream for the newly switched channel is transmitted (step S5).
[0058] The MPEG decoder 22 then also discards MPEG data for the
channel before input of a channel switching command, transmitted
from the AV server 1 in channel switching mode. Specifically, the
MPEG decoder 22, after changing to channel switching mode, discards
received data until MPEG data made up of one GOP consisting of only
one I picture is received, even if MPEG data is received from the
AV server 1.
[0059] It is possible to determine whether or not MPEG data
transmitted from the AV server 1 is MPEG data for the channel after
switching according to whether or not the one GOP of the received
MPEG data has only one I picture.
[0060] If channel select instruction information is received from
the AV client unit 2 (step S6), the control section 14 of the AV
server 1 outputs an instruction to switch to a new channel to the
TV tuner 11 (step S7). Also, the control section 14 controls to
stop encoding processing in the MPEG encoder 12, and to discard
data that has accumulated in the buffer memory 12a (step S8). At
this time, in the case where MPEG data for the original channel
that is not yet transferred remains in the network interface
section 13, that data is also discarded.
[0061] The TV tuner 11 changes channel select for the broadcast
station to be received based on the instruction from the control
section 14, and receives a broadcast signal for the new channel
broadcast station (step S9). The TV tuner 11 outputs a signal for
channel selection completion to the control section 14 when receipt
of a broadcast signal for the new channel broadcast station starts.
The control section 14 transmits a channel select completion signal
to the AV client unit 2, through the network interface section 13,
when the channel select completion signal is received from the TV
tuner 11.
[0062] After channel select completion, the MPEG encoder 12
commences encoding of the received broadcast signal (step S10).
Specifically, after commencing encoding, the MPEG encoder 12
initially creates an I picture from the broadcast signal, thereby
creating MPEG data where one GOP consists of only one I
picture.
[0063] Once the MPEG encoder 12 creates MPEG data having a GOP
consisting of only one I picture, the control section 14
immediately transmits the MPEG data from the network interface
section 13 via the network 3 to the AV client unit 2 (step
S11).
[0064] The MPEG decoder 22 of the AV client unit 2 receives MPEG
data having a GOP consisting of only one I picture from the network
interface section 21 and carries out decoding (step S12).
[0065] Once the MPEG decoder 22 decodes the MPEG data having one
GOP consisting of only one I picture, a decoded video signal is
immediately output to the video output section 23. The MPEG decoder
22 also stores the video signal (I picture video signal) in the
buffer memory 22a and outputs repeatedly to the video output
section 23 (step S13).
[0066] After the video signal has been output to the video output
section 23, the MPEG decoder 22 notifies that the MPEG data of a
GOP having only an I picture has been decoded and output to the
control section 25.
[0067] The video output section 23 outputs a video signal to the
display 4. As a result, a video signal (still picture)
corresponding to MPEG data having one GOP consisting of one I
picture is displayed on the display 4.
[0068] In the AV server 1, after the MPEG data having one GOP
consisting of one I picture has been transmitted to the AV client
unit 2, the MPEG encoder 12 continues with normal encoding. That
is, the MPEG encoder 12 creates following I pictures, P pictures
and B pictures, to create MPEG data for a normal GOP consisting of
these pictures (for example, 15 frames). The created MPEG data is
transmitted to the AV client unit 2, via the network 3, from the
network interface section 13 (step S14).
[0069] When the MPEG decoder 22 of the AV client unit 2 received
MPEG data for the next GOP after receiving MPEG data having one GOP
consisting of only one I picture, the MPEG decoder 22 stores
subsequent MPEG data in the buffer memory 221 thereof (step
S15).
[0070] The control section 25 monitors the amount of data of the
buffer memory 22a of the MPEG decoder 22 (step S16). If the data
amount of the MPEG data accumulated in the buffer memory 22a
reaches a predetermined data amount (for example, a data amount of
about half the data storage capacity of the buffer memory 22a) (Yes
in step S16), the processing mode of the MPEG decoder 22 is changed
to normal mode.
[0071] After change to normal mode by control of the control
section 25, the MPEG decoder 22 commences decoding of MPEG data
stored in the buffer memory 22a (step S17). In normal mode, the
MPEG decoder 22 discards MPEG data stored in the buffer memory 22a
in the order in which they are decoded.
[0072] FIG. 3 is a graph showing a lapse of time from channel
switching to start of image display for an AV system 100 according
to the first embodiment and an AV system of the related art. In
FIG. 3, time line (a) shows an example for an AV system of this
embodiment, while time line (b) shows an example for an AV system
of the related art.
[0073] At time A in FIG. 3, if the user inputs an instruction to
switch channel, control data (channel select instruction
information) representing a channel switching instruction is
transmitted from the AV client unit 2 to the AV server 1. Also, at
time B, the AV server 1 receives the channel switching instruction
transmitted from the AV client unit 2.
[0074] At time C, the TV tuner 11 of the AV server 1 carries out
switching, and at time D the initial GOP after the channel has been
switched is created. Then, at time E, the AV client unit 2 receives
the initial GOP data transmitted from the AV server 1. At time F,
the AV client unit 2 decodes the initial GOP data, and an initial
one picture is displayed on the display 4.
[0075] As shown in FIG. 3, with the AV system 100 of this first
embodiment, when there received an instruction to switch channel,
if a broadcast signal for the new channel is received, MPEG data
consisting of only an I picture is initially created, and
transmitted to the AV client unit 2. On the other hand, the AV
client unit 2 decodes the received MPEG data having only an I
picture, a decoded video signal is immediately output from the
video output section 23 to the display 4, and is displayed on the
display 4 as a still picture. At this time point, it is possible to
display for a user an image of a desired channel on the display 4
in a shorter period of time than with the AV system of the related
art (refer to time line (b)). After that, the still image is
preferably continuously output, and after that a moving picture
will be output.
[0076] As described above, in the first embodiment of the present
invention, when a channel switching instruction for an analog
broadcast is received from the AV client unit 2, the AV server 1
discards data being currently decoded and data stored in the buffer
memory 12a. Then, the AV server 1 creates MPEG data having one GOP
consisting of only one I picture from the broadcast signal for the
new channel, and immediately transmits this data to the AV client
unit 2. After transmitting the MPEG data to the AV client unit 2,
the AV server 1 performs normal encoding, and transmits MPEG stream
data to the AV client unit 2.
[0077] On the other hand, if the AV client unit 2 receives a
channel switching instruction, operating mode is changed to channel
switching mode, and data being currently decoded and data stored in
the buffer memory 22a are discarded. Then, if MPEG data having one
GOP consisting of only one I picture is received from the AV server
1, the MPEG data is decoded and immediately output from the video
output section 23 to the display 4. Therefore, at this time a still
image is displayed on the display 4. After that, when a
predetermined amount of the normally encoded data is stored in the
buffer memory 22a, the processing is returned to normal mode, where
a decoding of MPEG data stored in the buffer memory 22a is
commenced. A decoded video moving picture signal is output to the
display 4. In this way, after a still image has been displayed for
a predetermined period, a moving image corresponding to the
broadcast signal of the switched channel is displayed.
[0078] According to the above processing, in the AV client unit 2,
after receiving a channel switching instruction, a broadcast image
for the new channel is displayed on the display 4 in a short period
of time. Therefore, the user does not experience any disconcerting
of feeling when switching channels. Also, even when repeatedly
switching channels, since it is possible to see an image for the
selected channel on the screen in a short period of time,
operability perceived by the user is good. This is of particularly
benefit to users who like to change channels often.
[0079] With the above described first embodiment, after channel
switching, decoded still image data initially decoded by the AV
client unit 2 is displayed. However, this is not limiting, and it
is also possible to acquire and output still image data from the
buffer memory 22a each time a predetermined amount of data is
accumulated in the buffer memory 22a, or every predetermined
time.
[0080] Also, with the above described first embodiment, in the case
of channel switching, after output of a still image for a broadcast
signal of a new channel and the amount of data accumulated in the
buffer memory 22a of the MPEG decoder 22 has reached a
predetermined amount, normally decoded moving images are output.
However, it is also possible to sequentially decode MPEG data
accumulated in the buffer memory 22a until a predetermined amount
of data has accumulated in the buffer memory 22a, and output this
while interpolating frames of a decoded video signal.
[0081] In this case, after receiving a channel switching
instruction, if the control section 25 of the AV client unit 2
receives MPEG data having one GOP consisting of only one I picture
from the AV server 1, the data is decoded and displayed on the
display 4 as a still picture. Then, while storing MPEG data
transmitted consecutively from the AV server 1 (for example, MPEG
data where 1 GOP is made up of 15 frames) in the buffer memory 22a,
the stored MPEG data is sequentially decoded, and a decoded video
signal is output to the video output section 23.
[0082] While the MPEG decoder 22 interpolates frames of the decoded
video signal, the video output section 23 outputs an interpolated
video signal to the display device. As a method of interpolating
the video frames, for example, there is a method of outputting a
video signal decoded from MPEG data having 1 GOP consisted of 15
frames twice in one frame. Video signal interpolation is not
limited to twice in one frame, and it is also possible to
interpolate 3 or more times. In this way, a video signal output
from the video output section takes twice the playback time
compared to the original playback time (display time). According to
this constitution, a moving picture that appears to be being played
back in slow motion is displayed on the display 4.
[0083] Processing for interpolation of video signal frames carried
out by the video output section 25 is controlled by the control
section 25. The control section 25 monitors time for the video
output section 23 outputting an interpolated video signal to the
display 4, and controls the MPEG decoder 22 to decode MPEG data at
such a timing that the video signal is output from the video output
section without intervals.
[0084] Therefore, after initially decoding and outputting first
MPEG data having one GOP comprised of only one I picture, the MPEG
decoder 22 decodes second MPEG (MPEG data having one GOP made up of
15 frames) received consecutively with the first MPEG data and
outputs to the video output section 23. After the decoded video
signal has been output to the video output section, third MPEG data
transmitted consecutively from the AV server 1 is decoded and
output to the video output section 23 until the video output
section 23 completes output of an interpolated video signal
corresponding to the second MPEG data.
[0085] Since the video output section 23 interpolates and outputs
frames of the video signal, playback time of the video signal
output from the video signal output section 23 becomes longer than
the original playback time. As a result, the time from decoding of
particular MPEG data until decoding of the next MPEG data becomes
long, and MPEG data transmitted from the AV server is gradually
accumulated in the buffer memory 22a. Then, when the data in the
buffer memory 22a is accumulated to a predetermined amount, normal
decode processing commences.
[0086] Thus, immediately after a channel switching operation, a
still image for a broadcast signal of the new channel is displayed
on the display 1, and after that moving pictures are displayed in
slow motion, and finally a normal moving picture is displayed.
Specifically, after the channel switching operation, the playback
speed of the image signal for the new channel gradually increases
from a still image, so that eventually a normal moving picture is
displayed.
[0087] Accordingly, when a viewer performs channel switching and
watches a broadcast signal for the new channel, there is no sudden
change from a still image to a moving image, but a gradual change
from the still image to the moving image, which means that it
allows the user to watch the image without a disconcerting
feeling.
Second Embodiment
[0088] The following is a detailed description of an AV unit
according to a second embodiment of the present invention. With the
second embodiment shown in the following, description will be given
for digital recording and playback of an analog broadcast signal,
for example, a recording and playback unit known as a PVR (Personal
Video Recorder).
[0089] FIG. 4 is a diagram illustrating the structure of an AV unit
200 according to the second embodiment. The AV unit 200 functioning
as a recording and playback unit is provided with a TV tuner 30, an
MPEG encoder 31, an MPEG decoder 32, a storage section 33, a video
output section 34, a user interface section 35 and a control
section 36. In order to facilitate understanding, description for
sections that are the same as the structure shown in FIG. 1 will be
omitted.
[0090] The MPEG encoder 31 converts an analog image signal from the
TV tuner 30 to a digital signal by compression. The storage section
33 stores a digital signal from the MPEG encoder 31. The MPEG
decoder 32 reads out a compressed digital signal stored in the
storage section 40, and converts it to an analog image signal. A
decoded analog image signal is sent to the video output section 34
and output to a display etc.
[0091] In this AV unit 200, when data stored in the storage section
33 is read out an extremely short time after being stored, and is
then output, pseudo real time playback becomes possible. In more
detail, there are cases where data written in the storage section
33 by the MPEG encoder 31 is then immediately read out by the MPEG
decoder 32 and decoded. This is a case where, for example, playback
commences before completion of recording of an analog TV program
currently being recorded, specifically, during recording.
[0092] In the case that the user interface section 35 receives an
instruction to switch analog broadcast channel while playing back
in real time, the control section 36 shifts processing thereof to
channel switching mode, the same as with the above-described first
embodiment. Processing in that mode will be described in detail in
the following.
[0093] If the control section 36 acquires channel select
instruction information received by the user interface section 35,
frequency information for the channel to be switched to is sent to
the TV tuner 31. If switching to the instructed channel is
completed, the TV tuner 31 sends a signal indicating this to the
control section 36.
[0094] The control section also controls the MPEG encoder 31 to
discard data stored in the buffer memory 31a, and then to commence
encoding of a frequency signal for the newly selected channel. At
this time, the MPEG encoder 31 creates MPEG data having one GOP
consisting of one I picture and immediately outputs the MPEG data
to the MPEG decoder 32. After that, the MPEG encoder 31 creates
normal MPEG data and stores the data in the storage section 33.
[0095] When shifting to channel switching mode, the control section
36 also controls the MPEG decoder 32 to discard data stored in the
buffer memory 32a. After that the MPEG decoder 32 waits. If MPEG
data having one GOP consisting of only one I picture is received,
the MPEG decoder 32 immediately decodes the data decoded and
outputs a video signal corresponding to a still picture to the
video output section 34. Then, the MPEG decoder 32 commences
reading out of a MPEG data stored in the storage section 33.
[0096] If a sufficient amount of data has accumulated in the
decoder in the buffer memory 32a of the MPEG decoder 32, the
control section 36 controls to shift processing thereof from the
channel-switching mode to normal mode. That is, the control section
36 instructs commencement of normal mode to the MPEG decoder 32.
Accordingly, a still picture video signal is output to the video
output section 34 until acquisition of a video signal resulting
from decoding of MPEG data newly stored in the storage section
33.
[0097] According to the above described second embodiment, at the
time of pseudo real time playback, the user can see an image for a
newly selected channel immediately after analog broadcast channel
switching. Therefore, a disconcerting effect on the user is
reduced, and usability is improved.
[0098] With the above-described embodiment, a recording and
playback unit capable of pseudo real-time playback has been
exemplified. However, the present invention is not thus limited,
and may also be applied to all AV units that carry out
encoding/decoding processing on received analog broadcast signals
to output an image signal. For example, the present invention may
be applied to a broadcast signal-processing unit such as a
broadcast tuner having a structure as shown in FIG. 5, which does
not have the storage section 33 of FIG. 4. The present invention
may also be applied to broadcast signal display unit for TV, for
example, provided with a display section 37, such as shown in FIG.
6.
[0099] With the above-described first and second embodiment, MPEG
data made up of one GOP comprising of smaller numbers of pictures
than that of before receiving a channel switching instruction may
be used in stead of MPEG data made up of one GOP consisting of one
I picture. That is, when said switching instruction is received,
MPEG encoder 12 and 31 may create MPEG data made up of one GOP
comprising of smaller numbers of pictures than that of before
receiving said switching instruction. Similarly, MPEG decoder 22
and 32 may determine whether it is MPEG data after a channel
switching or not depending on whether or not they receive MPEG data
made up of one GOP comprising of smaller numbers of pictures than
that of before receiving said switching instruction. Furthermore,
received MPEG data made up of one GOP comprising of smaller numbers
of pictures than that of before receiving said switching
instruction may be decoded and output to display 4.
[0100] Although only some exemplary embodiments of this invention
have been described in detail above, those skilled in the art will
readily appreciate that many modifications are possible in the
exemplary embodiments without materially departing from the novel
teachings and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of the
invention.
[0101] The disclosure of Japanese Patent Application Nos. JP
2003-417138 filed on Dec. 15, 2003 and JP 2004-210022 filed on Jul.
16, 2004, including specification, claims, drawings and abstract is
incorporated herein by reference in its entirety.
INDUSTRIAL APPLICABILITY
[0102] The present invention is useful in providing AV units and AV
systems having high usability.
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